Advances in integrated circuit technology have led to faster clock frequencies and greater densities of transistors. These advances have resulted in a corresponding increase in the amount of heat generated by the integrated circuits (ICs). With large amounts of heat being generated, the problem of efficient heat dissipation has received increased attention.
Typically, either active or passive devices cool ICs and printed circuits boards (PCBs). An active cooling device is one that introduces additional power into the system being cooled, whereas a passive device does not introduce additional power. An example of a passive cooling device is a heat sink mounted onto an integrated circuit package. As is well known, passive cooling devices have a limited capacity to dissipate heat.
An active cooling device, on the other hand, can dissipate larger amounts of heat. An example of a simple active cooling device is a fan that blows air across a heat sink and/or an IC package body. But even though active cooling devices tend to work better than their passive counterparts, heat dissipation capacity is still limited. This means that for newer ICs and PCBs, which generate more heat, ever-larger heat sinks and greater airflow rates are required.
A recently introduced type of active cooling device is based upon the scientific principle known as the Peltier effect, first discovered in 1834. In the Peltier effect, current passing through the junction of two different types of conductors causes a temperature change across the junction. Modern active cooling devices have been built which utilize the Peltier effect to operate as a thermoelectric cooler. A typical thermoelectric cooling device comprises a number of P-type and N-type semiconductors that are connected electrically in series and sandwiched between two plates. Bismuth telluride is primarily used as the semiconductive material. When connected to a DC power source, the current causes heat to move from one plate of the thermoelectric cooler to the other. Naturally, this creates hot and cool plate sides of the thermoelectric cooler. An example of a thermoelectric cooling device for use with an integrated circuit package is described in U.S. Pat. No. 5,032,897 of Mansuria, et al.
FIG. 1 illustrates a thermoelectrically cooled integrated circuit package as disclosed in the Mansuria patent. Referring to FIG. 1, integrated circuit package 10 consists of an IC 14 connected to chip carrier module 13 via thermoelectric cooler 16. A thermoconductive layer 12 connects the module 13 to a heat sink 11. Input/output (I/O) pins 17 provide electrical connection via integrated circuit 14 of the bonding wires 20. In addition, conductors 18 and 19 provide power to thermoelectric cooler 16. The cavity that encloses the IC 14 within module 13 is hermetically sealed by lid 15.
When a DC voltage is applied via conductors 18 and 19 to thermoelectric cooler 16, heat is transferred from integrated circuit 14 to chip carrier module 13. The heat transferred to module 13 is then dissipated into the surrounding environment via heat sink 11.
One of the limitations of the prior art system shown in FIG. 1 is the difficulty of implementation, particularly at the manufacturing level. In particular, mounting of integrated circuit 14 to a wall of the chip carrier module cavity via thermoelectric cooler 16 must be performed by the semiconductor manufacturer. Generally speaking, this imposes a requirement that each module 13 be manufactured to include a heat sink 11 attached to the chip carrier module, as shown in FIG. 1. Thus, the original equipment manufacturer (OEM), or anyone else involved in assembling package 10 into a larger system, lacks the ability of selectively controlling IC temperature. In many instances, the package of FIG. 1 limits the overall cooling design at the system level.
It is desirable to be able to selectively control the temperature of ICs assembled onto a printed circuit board in a way that provides design flexibility to the OEM or board manufacturers. Such a system would result in lower cost and more efficient heat dissipation, especially at the system level.